Change the "used UVLayer" in all materials in texture_slot 0
i got it to work... wrong syntax was the problem :) i not used to program with python.

here is my solution:

import bpy
for item in bpy.data.materials:
     for itextures in item.texture_slots:
        if itextures is not None:
            item.texture_slots[0].uv_layer = "UVMap"